1. Field of the Invention
The invention relates to lift assemblies for semi-trailer axle/suspension systems, and in particular to axle/suspension system lift assemblies for semi-trailers which are convertible between highway and railroad use. More particularly, the invention is directed to an assembly which lifts semi-trailer slider axle/suspension systems when switching the trailer from use in a highway mode to use in a railway mode, wherein lifting of the axle/suspension system is accomplished without the use of air, and instead utilizes a relatively lightweight coil torsion spring which efficiently accomplishes the lifting operation through the use of a variable rate moment arm.
2. Background of the Invention
Tractor-trailers or semi-trailers having slider-mounted axle/suspension systems have been utilized for many years in applications where such trailers are transported over both roadways and railways. More specifically, these trailers are transported by a conventional tractor over roadways, usually short distances, between rail yards or between a rail yard and a destination where trailer cargo is dropped off or picked up. When the trailer is being used in the rail mode, which is its primary function, specialized rail bogies are used to support and adapt the trailer for railroad travel.
More particularly, when it is desired to convert the trailer to railroad use, the tractor backs the trailer, with its axle/suspension system at ride-height or in highway mode, in position adjacent to a rail bogie which is movably engaged with the railroad rails. To enable the rear end of the trailer to clear the bogie for attachment thereto, specialized high capacity air springs in the axle/suspension systems are overinflated to a rebound or transfer position to lower the axle/suspension system away from the trailer, or effectively raise the trailer frame and cargo deck. After the rear end of the raised trailer is positioned adjacent to the bogie and the trailer is backed into engagement with the bogie, the trailer air-ride axle/suspension system air springs are vented. When air is exhausted from each air spring, its respective torsion spring then is free to operate and lift the axle/suspension system to its upwardmost or rail position to clear the trailer tires of the rail. The above procedure obviates the need to lift trailers onto rail bogies with cranes and the like. Also, a plurality of trailers can be mounted on a train in this manner for transport as is well known to those skilled in the art.
Conventional compression springs heretofore have been utilized to accomplish lifting of the axle/suspension system to clear the trailer tires of the rails without the use of air, which is a requirement of the rail carrier. More particularly, pneumatically-operated lift assemblies are well-known but require air supplied by the tractor to operate properly. Since the trailer is disengaged from its tractor for rail use, that air is unavailable. Moreover, the railroads prohibit use of air from the train engine, which is reserved exclusively for braking of the train, and not for such lift assemblies, hence the need for an alternative lifting mechanism. Although such compression springs, which are longitudinally oriented relative to the trailer, satisfactorily perform the function of lifting an axle/suspension system, these springs are relatively inefficient in performing the lift procedure, in part due to their longitudinal orientation relative to the transversely extending axle, and thus must be robust/heavy which adds unwanted weight and cost to the trailer. In fact, a compression spring of the type customarily used in the described applications weighs about 36 pounds. Since railroad carriers require redundancy in such systems, each axle must have two lift springs, thereby adding about 72 pounds to each axle to be lifted on a trailer. Each slider typically has two axles that must be lifted, thus adding a total of about 144 pounds to the trailer in springs alone. Multiplying the number of trailers being transported by the train engine by 144, it can be seen that the added weight/cost is significant. This added weight also is a disadvantage for over-the-road travel.
Compression springs have additional disadvantages. Due to the robustness and weight of such springs, a larger, more robust and expensive air spring is required. More specifically, in order to overcome the bias of the compression spring to lower the axle/suspension system during the operation described hereinabove for transferring the trailer from the tractor to the rail bogie, the higher capacity specialized air spring must be overinflated to a full rebound position of about nine inches from the ride height position, as compared to the full rebound position of about four and one-half inches for an air spring used in a roadway-only trailer air-ride axle/suspension system. However, it is understood that such compression springs do eliminate the need for shock absorbers in the axle/suspension system, since the spring is active at all times and provides suspension damping during roadway use of the trailer.
Thus, a long-felt need has existed for a relatively lightweight and low-cost non-air operated trailer axle/suspension system lift assembly for railroad applications, which nonetheless exhibits more efficient lift capacity without the necessity of a more robust and expensive air spring for lowering the axle/suspension system. The present invention solves the problems of prior art lift assemblies having compression springs, by utilizing a torsion spring to lift the axle/suspension system. The transversely oriented torsion spring exhibits more efficient lifting properties despite its lighter weight and lower cost, yet requires a less robust and lest costly customized air spring than prior art lift assemblies to overcome the bias of the torsion spring when lowering the axle/suspension system, due to the incorporation of a variable rate moment arm into the lift assembly.
Objectives of the present invention include providing a lift assembly for a semi-trailer slider axle/suspension system, which is capable of lifting the system to an upwardmost or rail position without the use of air.
Another objective of the present invention is to provide such a lift assembly having increased lifting efficiency over prior art lift assemblies, but which also minimizes the force required by the air spring to lower the axle/suspension system to the rebound or transfer position.
An additional objective of the present invention is to provide such a lift assembly which provides suspension damping for over-the-road use of the trailer and eliminates the need for suspension assembly shock absorbers.
Still another objective of the present invention is to provide such a lift assembly which is economical, lightweight, durable in use, easy to install, maintain, and replace.
These objectives and advantages are obtained by the lift assembly of the present invention for an axle/suspension system of a vehicle, the lift assembly including, a coil torsion spring having a pair of ends, means for capturing the spring ends, the means including a rotatable plate operatively engaged with a selected one of the spring ends, a link having upper and lower ends, the link being pivotally attached at its upper end to the rotatable plate and at its lower end to the axle, so that an air spring of the axle/suspension system can overcome the bias of the torsion spring to lower the system, and upon deflation of the air spring the torsion spring can lift the system to a desired height and maintain the system in the lifted position.